This section introduces aspects that may facilitate better understanding of the present disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
In a mobile telecommunication network, a user equipment (UE) may access various services by connecting to a core network (CN) via a radio access network (RAN). However, the access to services may fail due to various reasons.
For example, due to differences of UEs in processing capability, memory capacity, hardware performance, or embedded operation system etc. or various UE categories defined in standard specifications, e.g. the third generation partnership project (3GPP) specifications, some UEs are incapable of some kind of services that require specific capabilities. The incapability of these UEs is unknown to the RAN or even CN Therefore, when these UEs try to access such a kind of services, a service failure usually occurs although the UEs may successfully access the RAN and CN.
For another example, incorrect settings in a UE, e.g. wrong Access Point Name (APN) may result in a Non-Access Stratum (NAS) failure while a RAN connection is successfully established, which may also cause the access to services to fail.
A user of a UE may subscribe various application services and the UE may have some specific applications installed therein, some of which may trigger the UE to automatically access the RAN at a specific time, of which the user is not aware. In this case, if the service traffic gets failed due to the capability limitations or wrong settings as mentioned above, or other reasons, e.g. the application server itself being down, the UE being out of credit or the UE's performance being too low etc., the UE that has the specific applications installed therein, may keep trying access to the RAN, and enter an endless loop until the user manually stops it. In another case, some UEs may be maliciously used to continuously attempt the access procedure even though access to the RAN has succeeded. The UEs in the above two cases may be regarded as being abnormal.
FIG. 1 illustrates an example signaling flow of an abnormal UE for trying to access the CN in a Wideband Code Division Multiple Access (WCDMA) network. In this example, the RAN access is successful, while a NAS failure occurs due to a wrong APN, for example. However, after the NAS failure, the UE sends an RRCConnectionRequest again and starts another RAN access attempt. This access attempt may be repeated until the cause for the NAS failure is eliminated.
FIG. 2 illustrates an example signaling flow of an abnormal UE for accessing an application layer server in a 3GPP long term evolution (LTE) communications network. In this example, the UE has successfully accessed the RAN and CN, while a service failure occurs for the application layer server is down, for example. However, after the service failure, the UE sends an RRCConnectionRequest again and starts another RAN access attempt. This access attempt may be repeated until the cause for the service failure is eliminated.
Abnormal UEs may lead to several disadvantages. For example, an abnormal UE may consume RAN resources, especially those on the air interface and take up network capacity meaninglessly. In order to handle its access attempt, both common channels and dedicated channels are occupied. Taking a WCDMA network as an example, a Radio Network Controller (RNC) may also need to initialize NAS connections toward the CN. Therefore, the abnormal UEs corrupt the operator's RAN capacity and weaken the robustness against radio congestion. Furthermore, abnormal UEs also waste resources in the CN, e.g. resources on a Serving Gateway Support Node (SGSN) and Gateway GPRS (General Packet Radio Service) Support Node (GGSN) in a WCDMA network. Moreover, for an abnormal UE with a NAS failure, the RAN accessing procedure appears normal; and for an abnormal UE with an application service failure, all Key Performance Indices (KPIs) appear normal. This makes it difficult for operators to detect the problem and take further actions.
There is an existing patent application CN102143552A, which proposes to prevent the access attempt of a UE after it has experienced a predetermined number of RAN access failures within a certain time period. However, this solution is based on the RAN access failure number and thus does nothing with the above mentioned problems in which the RAN access may always be successful.
3GPP technical specification (TS) 36. 331 defines an “access barring check”, according to which, a message is broadcasted in SystemInformationBlock Type 2 towards all UEs to inform UEs to wait for a random time period before a next access attempt after the previous RAN access failure. However, this solution is also based on the RAN access failure, and thus does nothing with the above mentioned problems in which the RAN access may always be successful.